The Chaucer astrolabe

The astrolabe is a multi-functional instrument
which enables the user to perform such diverse tasks as timekeeping
at day and night, surveying, determining latitude, and casting
horoscopes.

Geoffrey
Chaucer (about 1342-1400), better known for his
Canterbury Tales, also
wrote a treatise on the astrolabe which was widely disseminated.
The type of astrolabe he described matches the features of this
instrument, with its distinctive Y-shaped
rete,
a dog's head as a star-pointer for Sirius (known as the
dog-star), and other star-pointers in the shape of birds. The frame
around the circumference has a dragon's head and tail
respectively at the
ends.

Three of the saints
mentioned in the calendrical list on the back are of particular
English significance, and one of the
latitude plates
is marked for Oxford, while the others are laid out for Jerusalem,
'Babilonie', Rome, Montpellier, and
Paris.

F.A.B. Ward, Catalogue of European scientif (London, The British Museum Press, 1981)